The present application relates generally to apparatus and methods for detecting arc faults, and more specifically to arc fault detection apparatus and methods that are less susceptible to nuisance tripping.
Arc fault detection apparatus and methods are known that employ a micro-controller to measure voltages associated with a load, and to process data representing the voltage measurements to determine the presence of electrical arcing. For example, a conventional arc fault detection apparatus may be configured to sense an alternating load current, to filter and rectify the AC signal, and to provide the rectified signal to an integrating capacitor. The conventional arc fault detection apparatus may then use a micro-controller to take measurements of the voltage across the integrating capacitor, and to convert the voltage measurements to digital data for subsequent processing by an algorithm. For example, the algorithm may be employed to analyze the measured voltage levels corresponding to respective cycles of the line voltage, and to determine whether the voltage measurements are characteristic of electrical arc faults or nuisance loads such as dimmer loads, appliance thermostat switching, drill current transitions, random line voltage spikes, and/or EMI bursts. In the event the voltage measurements are characteristic of an arc fault, the conventional arc fault detection apparatus typically trips a circuit breaker to disconnect the power line from the circuit.
Although the above-described conventional arc fault detection apparatus has been successfully employed to detect and distinguish between electrical arcing and nuisance loads, there is a need for arc fault detection techniques that have increased reliability. For example, due to the generally chaotic nature of electrical arcing, arc faults typically produce varying numbers of arcing events per half cycle of the line voltage. In contrast, nuisance loads, e.g., triac-controlled dimmer circuits, typically produce the same number of arcing events per half cycle, and may therefore produce arcing events periodically over multiple half cycles. However, conventional arc fault detection apparatus often cannot reliably distinguish between periodic and non-period arcing events, and are therefore prone to nuisance tripping. Moreover, such conventional apparatus frequently have difficulty distinguishing between certain start-up and shutdown conditions and electrical arcing. In addition, although some loads may produce noisy switching signals having relatively large voltage levels, such signals are not necessarily indicative of electrical arcing and may be incorrectly characterized as arc faults by conventional arc fault detection apparatus.
It would therefore be desirable to have improved arc fault detection apparatus and methods that avoid the drawbacks of the above-described conventional apparatus and methods.